Rapid deployment subsea chemical injection system

ABSTRACT

A rapid deployment, subsea chemical injection skid assembly includes a non-buoyant skid lowered on a weight bearing line from a surface vessel. The skid carries a chemical injection pump, as well as at least one chemical tank in fluid communication with the chemical injection pump. The skid assembly may include a recirculation/mixing system to limit separation or solids drop out of chemicals arising from medium or long-term storage of chemicals in the chemical tank. The skid assembly may include a seawater filtration system to supply seawater for mixing with chemicals prior to injection. The skid assembly is operable by a separately tethered remotely operated vehicle.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of the filing date of, and priorityto, U.S. Application No. 62/738,575, filed Sep. 28, 2018, the entiredisclosure of which is hereby incorporated herein by reference.

This application also claims the benefit of the filing date of, andpriority to, International Application No. PCT/US2018/068156, filed Dec.31, 2018, the entire disclosure of which is hereby incorporated hereinby reference.

TECHNICAL FIELD

The disclosure relates, in general, to hydrocarbon production, and moreparticularly, to subsea facilities utilized in the production ofhydrocarbons. Most particular, the disclosure relates to a rapiddeployment chemical injection skid system and method for injection ofchemicals in subsea hydrocarbon production facilities.

BACKGROUND

Subsea systems for the production of hydrocarbons such as oil and gasrequire injection of various chemicals into their production facilities.The chemicals typically improve production capacity and/or inhibitagainst corrosion, wax, asphaltene, hydrates, scale or other issues.

Normally the chemical injection system is incorporated into the designof the production facility and is installed and operated as an integralpart of the production facility. Chemicals are typically pumped from asurface facility such as a floating production vessel, offshoreplatform, or onshore plant, through an umbilical system, entering thesubsea system at the wellhead, pipeline end termination (PLET) subseamanifold or other apertures.

Some production facilities require subsea chemical injection in additionto the installed facilities or injection of specialized chemicals, whichcannot be injected from surface through a long umbilical. There areexisting subsea chemical injection systems, designed for permanentinstallation, these typically have a high capital cost and a lead-timeof many months.

In some cases there is a need for rapid deployment of chemical injectionto a subsea facility for a relatively short duration; there may beuncertainty on the effectiveness of a chemical treatment; and/or shortremaining field life of the subsea facility.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure and theadvantages thereof, reference is now made to the following briefdescription, taken in connection with the accompanying drawings anddetailed description:

FIG. 1A is a schematic view of rapid deployment chemical injectionsystem deployed from a vessel to carry out chemical injection in subseahydrocarbon production facilities on the seabed.

FIG. 1B is a schematic view of rapid deployment chemical injectionsystem suspended from a vessel to carry out chemical injection in subseahydrocarbon production facilities within a wellbore.

FIG. 2A is a schematic view of a rapid deployment chemical injectionsystem with a line having a stab to be connected to a hot stab on thesubsea hydrocarbon production facility by a remote operated vehicle tocarry out chemical injection in subsea hydrocarbon production facilitieson the seabed.

FIG. 2B is a schematic view of a rapid deployment chemical injectionsystem with a line having a stab to be connected to a hot stab on thesubsea hydrocarbon production facility by a remote operated vehicle tocarry out chemical injection in subsea hydrocarbon production facilitieswithin a wellbore.

FIG. 3 is a perspective view of the chemical injection skid of the rapiddeployment chemical injection system of FIG. 1.

FIG. 4 is an elevation view of the chemical injection skid of the rapiddeployment chemical injection system.

FIG. 5 is a plan view of the chemical injection skid of the rapiddeployment chemical injection system.

FIG. 6 is an end elevation view of the chemical injection skid of therapid deployment chemical injection system.

FIG. 7 illustrates a method for injecting chemicals into a subseahydrocarbon production facility.

DETAILED DESCRIPTION

Disclosed herein are embodiments of a subsea chemical injection skidassembly that will permit the rapid deployment and injection ofchemicals to hydrocarbon production facilities located subsea. Carriedon the skid is a high accuracy chemical injection pump, as well as atleast one chemical tank in fluid communication with the chemicalinjection pump. The skid is connected to the production facilities usinga remotely operated vehicle (ROV) deployed from a vessel.

A control panel may be provided for manipulation by the ROV. Thechemical injection pumps can be powered by the ROV for short-term trialor pilot schemes of a few hours or days in length. For longer-termapplications, which may run many days or months, the pumps may be drivenelectrically via an umbilical (existing or installed system whichprovides power from the host facility) and/or by batteries, generatorsor by a variety of power sources.

In some embodiments, the skid may be lowered down and deployed close toa chemical injection point with or without intervention from an ROV. Ineither case, once deployed, the ROV is used to carry a hose from theskid and connect it to the injection point on the wellhead, PLET ormanifold or other location. In another embodiment, the skid may includea manipulator arm to connect the skid to the injection point. In one ormore embodiments, the pump is a high accuracy chemical metering pumpwhich allows pumping of very viscous and long chain chemical types.

As used herein, references to tanks include any chemical storage vessel.

In one or more embodiments, the skid may include two or more tanks fortwo or more separate chemicals, with each chemical stored in a separatetank. Each of the chemicals may be selected for evaluation of theeffectiveness with respect to a particular task involving the productionsystem. Thus, for any particular operation, multiple chemicals can betested in order to identify the most appropriate chemical for theoperation. In some embodiments, with multiple tanks on board the skid,this can occur in a single trip without the need for multiple trips.However, in other embodiments, it will be appreciated that because thechemical injection system is rapidly deployed and retrievable, thesystem may be retrieved to the surface; the chemicals on-board switchedout; and the system rapidly redeployed in order to permit suchevaluation, a method not possible by the prior art systems. Thus, themost appropriate chemical for a particular task can be readilyidentified.

In one or more embodiments, the chemical tank or tanks may be carried onthe skid on a first lower level and the chemical injection pump, as wellas manifolds, valving and other equipment may be carried on the skid ona second upper level, above the chemical tank o the first level.

The pump may be operated from a variety of power sources, including ROVhydraulic or electrical power for short duration tests/trials andprojects; electrical or hydraulic power via existing subsea umbilicalfrom the host facility; temporary downline from surface vessel or powerbuoy; batteries; generators, driven by sea current, product flow orother means; or a combination of the above (for instance battery powermay be used to meet high motor startup current, with running currentprovided via an umbilical).

In one or more embodiments, the skid may include a recirculation systemand/or mixing system to allow medium or long-term storage of chemical,avoiding separation or solids drop out. This is particularly necessaryfor chemicals such as highly viscous chemicals or chemicals formed oflong chain molecules.

The skid may also include a seawater filtration to supply seawater formixing with chemicals prior to injection.

In one or more embodiments, the skid may include manifolds to allow theconnection of additional or external chemical tanks. A manifold may alsobe utilized to refill onboard tanks.

In one or more embodiments, the chemical injection system is disposed tooperate using multiple power sources, such as a first power source forstartup and a second power source for on-going operation. In otherembodiments, the chemical injection system may scavenge power fromexisting subsea umbilical systems.

In one or more embodiments, the skid has mud mats which can be fitted onthe base, to prevent sinking in soft soil condition. The mud mats may beremoved for transportation and storage. The mud mats are particularlydesirable in certain embodiments because of the significant additionalweight added to the system by virtue of the fully charged chemicaltanks.

In FIG. 1A, a host facility 16 is positioned above a subsea hydrocarbonproduction facility 10. A chemical injection system 20 is launched fromthe host facility 16 and lowered to a location on the sea floor 18 neara chemical injection point of the hydrocarbon production facility 10,such as a wellhead or subsea manifold. As used herein, hydrocarbonproduction facility 10 may generally refer to any subsea system used inthe production of hydrocarbons, including any one or more of thewellbore, downhole equipment, wellhead, manifolds, pipelines, or risers.As used herein, host facility 16 may include a platform on the surface,a floating vessel, a floating production storage and offloading (FPSO)unit or an onshore system. Likewise, as used herein, manifold is used asa generic term to refer any wellhead trees, pipeline end manifolds(PLEMs), and pipeline end terminators (PLETs), to name a few, to carryout chemical injection. More specifically, chemical injection system 20is lowered by cable 22 above and in the vicinity of an injection point12 of the hydrocarbon production facility 10. In FIG. 1A, a hydrocarbonproduction facility 10 is a deep-water pipeline which lies on or nearthe sea floor 18 between manifolds, such as a PLEMS 14, either of whichmay be chemical injection point 12.

In one or more embodiments, chemical injection system 20 comprises anon-buoyant structure 21, the weight of which must be supported by cable22. In some embodiments, non-buoyant structure 21 may include a metalframe that functions as a platform to support one or more chemicaltanks, and a chemical injection pump. Additionally, the frame maysupport chemical metering equipment, valving and the like. The frame maysupport one or more electric or hydraulic motors that drive one or morechemical injection pumps. The cable 22 may be an umbilical cord that canprovide, either alone or in combination with other power sources,electric current for electric motors(s) or hydraulic power to drive thechemical injection system 20. In some embodiments, cable 22 is a cranewire deployed from host facility 16 and which cable 22 may bedisconnected from the non-buoyant structure 21 once it is positioned onthe sea floor 18. In other embodiments, cable 22 is an integralcomponent of non-buoyant structure 21, where integral cable 22 may beused for one or more of deployment, recovery, supply of electrical orhydraulic power, control, feedback and monitoring.

Because of the weight of the chemical tanks and the length of manychemical injection operations, it will be appreciated that it isundesirable to suspend chemical injection system 20 from cable 22 duringsuch operations. Rather, chemical injection system 20 is positioned onsea floor 18 near the chemical injection point 12 of hydrocarbonproduction facility 10. However, in other more abbreviated chemicalinjection operations, chemical injection system 20 may be suspendedabove sea floor 18 in the vicinity of the chemical injection point 12 ofhydrocarbon production facility 10.

FIG. 1B is similar to FIG. 1A, but in FIG. 1B production facility 10 isshown as a wellhead 11 positioned over a wellbore 13 with productionequipment 15 deployed therein. Wellhead 11 may include blowoutpreventers 17 or other equipment. Production equipment 15 is not limitedby the disclosure, but will be understood to be any equipment deployedin wellbore 13 to facilitate production of hydrocarbons from formation19, including, without limitation, pumps, upper production equipmentand/or lower production equipment. Similarly, host facility 16 ispositioned above wellhead 11 and a chemical injection system 20 islaunched from host facility 16 and lowered to a location on the seafloor 18 near wellhead 11, where chemical injection system 20 may beutilized to inject a chemical into wellbore 13 or wellhead 11 for aparticular task. In the illustrated embodiment, wellhead 11 is achemical injection point 12 for production facility 10.

Again, in one or more embodiments, chemical injection system 20comprises a non-buoyant structure 21 which may include a metal framethat supports one or more chemical tanks, and one or more chemicalinjection pumps. Additionally, the frame may support chemical meteringequipment, valving and the like. The frame may support one or moreelectric or hydraulic motors that drive the one or more chemicalinjection pumps. The cable 22 may be an umbilical cord that can provide,either alone or in combination with other power sources, electriccurrent for the electric motor(s) or hydraulic power to drive thechemical injection system 20.

Turning to FIG. 2A, chemical injection system 20 is lowered by a cable22 above and in the vicinity of PLEM 14, which is illustrated as achemical injection point 12. Chemical injection system 20 is designedspecifically for injection of chemicals to enhance hydrocarbonproduction. Chemical injection system 20 includes a non-buoyant skid 23having a frame 24. The frame 24 may support an electric, hydraulic orelecro-hydraulic motor 26 which powers chemical injection pump(s) 30that pumps chemicals into chemical injection point 12. A chemicalconduit or line 35 having a stab for connecting to chemical injectionpoint 12 in PLEM 14 transfers chemicals to PLEM 14. Chemical injectionsystem 20 may further include a remote operating vehicle (ROV) 40 usedto stab line 35 into chemical injection point 12. The ROV 40 has its ownumbilical cable 42 which is shown connected to a tether managementsystem (TMS) 44. The ROV's gripper 46 is manipulated to open and shutvalves on the chemical injection system 20 to perform the operationaltasks of injecting chemicals as described herein. It will be appreciatedskid 23 is lowered and deployed independently of ROV 40. Moreover, thecollective components of skid 23 render skid non-buoyant so that theweight of skid 23 must be supported by cable 22. In some embodiments,frame 24 may be weighted or constructed of materials that render skid 23non-buoyant, while in other embodiments, the equipment carried by frame24 render skid 23 non-buoyant.

In some embodiments, an on-board power supply 27 is also carried byframe 24. On-board power supply 27 may be a generator or batteries oranother local power source. In some embodiments, cable 22 is an electricumbilical. In some embodiments where motor 26 is electric, power issupplied to motor 26 either through cable 22 or from on-board powersupply 27. In other embodiments, both cable 22 and power supply 27 maybe used at different times to operate electric motor 26. For example,power supply 27 may be utilized to power electric motor 26 at start-upand power from cable 22 may be utilized to operate electric motor 26once pump 30 is in operation. In yet other embodiments, power toelectric motor 26 may be supplied by ROV 40, either directly from anon-board power source on ROV or from TMS 44 shown suspended from anumbilical cable 42. Finally, in yet other embodiments, electric motor 26may be eliminated altogether and pressurized hydraulic fluid from ROV 40may be utilized to operate pump 30.

Frame 24 also supports at least one chemical tank 28. In someembodiments, frame 24 may support two or more chemical tanks, such astanks 28 a and 28 b shown in FIG. 2A. In one or more embodiments, tank28 may be a bladder tank, having a liquid contained by a flexiblemembrane or bladder which can expand and contract to allow filling andremoval of chemicals in a subsea environment.

In one or more embodiments, the chemical tank or tanks 28 may be carriedon the skid 23 on a first lower level 32 and the chemical injection pumpand other equipment, such as electric motor 26, as well as manifolds,valving and other equipment, may be carried on the skid 23 on a secondupper level 34, above the chemical tanks 28 of the first level 32.

The chemical contained within a tank 28 carried on skid 23 may be achemical selected for a particular chemical injection task or operation,such to improve production capacity, to treat or inhibit againstcorrosion; to treat or inhibit wax; to inhibit asphaltene; to inhibithydrates; to treat or inhibit scale. In one or more embodiments, twodifferent chemicals or formulations for any one such task may bedeployed in separate tanks and skid 23 may be utilized to try theeffectiveness of each of the two chemicals for the task in order toevaluate which of the two chemicals is more effective. Thereafter, themore effective chemical may be deployed in a more long-term chemicalinjection solution. In this regard, in certain chemical injection tasks,two types of chemicals may be required for the task, and hence the needfor two or more tanks.

In other chemical injection tasks, it may be desirable to compare theeffectiveness of two different chemicals or treatments to identify whichchemical is best suited for a task. Thus, multiple tanks allow thetesting of multiple chemicals without the need to deploy skid 23multiple times, whether the chemicals are the same chemical withdifferent formulations or different chemicals altogether.

In one or more embodiments, a chemical preparation system 36 is alsocarried by frame 24. In some embodiments, chemical preparation system 36is a recirculating pump or mechanism that may be utilized to recirculatechemicals such as emulsions or where solids are suspended in a liquid,thereby ensuring that mixtures do not separate or that solids do notsettle out. This system 36 will maintain the chemical in a well-mixed,cohesive state and reduce separation of the components due to differingspecific gravities.

In some embodiments, chemical preparation system 36 is a mixing systemor mechanism that may be utilized to mix chemicals from two or moretanks 28 together before injection into PLEM 14. Thus, a first chemicalmay be contained in chemical tank 28 a and a second chemical may becontained in tank 28 b and system 36 may be utilized to mix the firstand second chemicals prior to injection.

In either of the foregoing descriptions, chemical preparation system 36may include a pump in fluid communication with a tank 28 and used todraw a chemical from the bottom of a tank 28, such as a bladder tank,and return the chemical to the top of the tank, or top of the bladderwithin tank 28, as the case may be. Thus, one or more of the tanks 28may have a first port for the withdrawal of chemicals and a second portfor injecting the chemicals back into tank 28. The first port may belocated at or near the bottom of the tank 28 and the second port may belocated at or near the top of the tank 28. In other embodiments, system36 may include an Archimedes screw within a tube, driven by a slow speedmotor, drawing chemical in at the base of the tube from the bottom ofthe tank or bladder, and discharging at the top of the tube andcascading onto the top of the chemical in the bladder.

It will be appreciated that pump 30 as described herein may be muchsmaller and lighter than high pressure hydrostatic testing pumps or aboost pump used for pigging. Rather, pump 30 is designed to pump andmeter low volumes of viscous or long chain chemical formulations. Thus,in contrast to other types of pumps for other operations, pump 30 may bea high accuracy pump, such as a positive displacement metering typepumps or rotary gear pumps or linear piston/syringe type pumps, which,monitors pump/motor rotation in order to determine the volume ofchemical pumped and flowrate. It will be appreciated that such smallerpumps are more readily driven hydraulically by ROV hydraulics for theshort-term application and/or electrically as described above.

FIG. 2B is similar to FIG. 2A, but FIG. 2B illustrates chemicalinjection system 20 being lowered by a cable 22 above and in thevicinity of wellhead 11 positioned over a wellbore 13 with productionequipment 15 deployed therein and used for the production ofhydrocarbons from formation 19. Wellhead 11 may include blowoutpreventers 17 or other equipment. Skid 23 is shown as constructed of aframe 24, which may have a first lower level 32 and a second upper level34. Frame 24 supports a chemical injection pump 30 and one or more tanks28. Frame 24 may support an electric motor 26 which powers a hydraulicmotor that provides high pressure hydraulic fluid for powering chemicalinjection pump 30 that pumps chemicals from the one or more tanks 28,such as tanks 28 a, 28 b, into wellhead 11 via line 35. ROV 40 is usedto stab line 35 into wellhead 11 utilizing gripper 46. ROV 40 issuspended from TMS 44 which has its own umbilical cable 42 through whichpower may be supplied to ROV 40, and in some embodiments, to electricmotor 26 of skid 23 as described above.

In some embodiments, on-board power supply 27 is also carried by frame24.

In one or more embodiments, a recirculating or mixing system 36 is alsocarried by frame 24.

Turning to FIG. 3, chemical injection system 20 is shown suspended fromcable 22. Specifically, chemical injection system 20 includes a skid 23formed of a frame 24 having a first lower level 32 and a second upperlevel 34. A tank 28 is shown on lower level 32. Chemical injectionsystem 20 also includes a control panel 41 into which an ROV (not shown)can stab for various operations.

In one or more embodiments, skid 23 may include a mud mat assembly 48extending from frame 24. Mud mat assembly 48 may include one or more mudmats 50 extending outward from a lower portion of frame 24, such aslower level 32. In the illustrated embodiment, mud mats 50 extend aroundthe perimeter of lower level 32 of skid 23 and are supported by a frame52. Preferably, mud mats 50 are generally horizontal when skid 23 issuspended from cable 22. It will be appreciated that mud mats 50 are notlimited to a particular structure, but may be any structure extends fromskid 23 to provide stability to skid 23 to prevent sinking in soft soilcondition. For example, mud mats 50 may be flat, or corrugated plates orscreen. The mud mat assembly 48 may be detachable from frame 24 fortransportation and storage. The mud mat assembly 48 is particularlydesirable in certain embodiments because of the significant additionalweight added to the chemical injection system 20 by virtue of the fullycharged chemical tanks 28. In this regard, because skid 23 is lowered tothe sea floor independently of the ROV, mud mat assembly 48 assists inensuring that chemical injection systems 20 remains correctly orientedduring operation.

FIG. 4 is an elevation view of chemical injection system 20 shownsuspended from cable 22. In this particular embodiment, cable 22 is notutilized as an umbilical for power supply. In any event, frame 24 ofskid 23 supports a chemical injection pump 30 and a first chemical tank28 a and a second chemical tank 28 b. A recirculating or mixing system36 is also carried by frame 24. Similarly, a control panel 41 is showninto which an ROV (not shown) may stab for an operation. For example,ROV may stab into control panel 41 to provide high pressure hydraulicfluid to operate (via a hydraulic motor) chemical injection pump 30 orto operate system 36. Chemical tanks 28 a, 28 b are supported on a firstlower level 32, while chemical injection pump 30, recirculating ormixing system 36 and control panel 41 are supported on a second upperlevel 34 above tanks 28.

A mud mat assembly 48 extends from frame 24. Mud mat assembly 48includes one or more mud mats 50 extending outward from first lowerlevel 32. Mud mats 50 are supported by a mud mat frame 52 and are shownextending generally horizontally from skid 23.

FIG. 5 is a top view of chemical injection system 20. Frame 24 of skid23 supports a chemical injection pump 30 and a chemical tank 28. Arecirculating or mixing system 36 may also be carried by frame 24.Similarly, a control panel 41 is shown into which an ROV (not shown) maystab for an operation. For example, ROV may stab into control panel 41to provide high pressure hydraulic fluid to operate (via a hydraulicmotor) chemical injection pump 30 or to operate system 36. A mud matassembly 48 extends from frame 24. Mud mat assembly 48 includes one ormore mud mats 50 extending outward from first lower level 32. Mud mats50 are supported by a mud mat frame 52 and are shown extending generallyhorizontally from skid 23.

FIG. 6 illustrates another embodiment of chemical injection system 20.In this embodiment, chemical injection system 20 is shown suspended fromcable 22. In this particular embodiment, cable 22 is not utilized as anumbilical for power supply. In any event, frame 24 of skid 23 supports achemical injection pump 30 and a first chemical tank 28 a and a secondchemical tank 28 b. A control panel 41 is shown into which an ROV (notshown) may stab for an operation. Chemical tanks 28 a, 28 b aresupported on a first lower level 32, while chemical injection pump 30and control panel 41 are supported on a second upper level 34 abovetanks 28.

A mud mat assembly 48 extends from frame 24. Mud mat assembly 48includes one or more mud mats 50 extending outward from first lowerlevel 32. Mud mats 50 are supported by a mud mat frame 52 and are shownextending generally horizontally from skid 23.

In this embodiment, chemical injection system 20 includes a seawaterfiltration system 56, which may include seawater filters, seawater flowcontrol and a seawater pump. It will be appreciated that in certainchemical injection operations, the chemicals may require to be dilutedwith seawater prior to injection. In some embodiments, such a system mayfurther include a boost pump and/or high pressure pump to provide thedilution water where such pumps may already be on board skid 23 forother purposes.

In operation, a method 100 for injecting chemicals into a subseahydrocarbon production facility is illustrated in FIG. 7. In a firststep 102, a skid carrying a chemical injection pump and chemical tank islowered to a subsea location adjacent a hydrocarbon production facility.In some embodiments, at least two chemical tanks are carried by the skidand lowered as part of the skid. The skid is non-buoyant and as such,the weight of the skid is supported by a cable deployed from a platformor vessel. In one or more embodiments where the chemical injectionoperations are to continue for a more extended period of time, such asdays or months, the subsea location is on the sea floor adjacent thehydrocarbon production facility. Once in position on the sea floor, thecable may be released, or alternatively, tension on the cable may bereleased in those instances where the cable also functions to provideelectrical power and/or hydraulic fluid to the skid. In otherembodiments, where the chemical injection operation is of only a shortduration, such as hours, the skid may continue to be supported by thecable by suspending the skid above the sea floor adjacent thehydrocarbon production facility.

In a second step 104, an ROV is utilized to attach a chemical injectionline in fluid communication with the chemical injection pump to aninjection point of the hydrocarbon production facility. The ROV istethered on an umbilical cable separate from the weight bearing cableutilized to lower the skid. In any event, the ROV attaches the chemicalinjection line to a chemical injection point, such as a manifold orwellhead of hydrocarbon production facility.

In step 106, a first power source may be utilized to initiate start-upof the pump and thereafter, a second different power source may beutilized to continue operation of the pump during pumping, it beingappreciated that a pump may draw more power during start up, but requireless power during on-going operation. The first power source is selectedfrom the group consisting of an on-board power source carried by theskid, an electrical cable extending from a surface vessel and powersupplied by the ROV; and the second power source is selected from thegroup consisting of an on-board power source carried by the skid, anelectrical cable extending from a surface vessel and power supplied bythe ROV.

In any event, at step 108, once the chemical injection line has beenattached to the chemical injection point and the pump has been poweredup, the chemical injection pump is operated to inject the chemical fromthe chemical tank into the subsea hydrocarbon production facility. Inthis regard, the chemical may be introduced into a manifold, a wellhead,or directly into a wellbore.

In step 110, the chemical is utilized to conduct a particular chemicaltreatment operation. Thus, the pump may be operated to treat productionequipment within a wellbore. In other embodiments, the pump may beoperated to improve production capacity of the hydrocarbon productionfacility. In other embodiments, the pump may be operated to treat orinhibit corrosion in the hydrocarbon production facility. In otherembodiments, the pump may be operated to inject the chemical from thechemical tank into a subsea manifold or pipeline system. In otherembodiments, the pump may be operated to treat or inhibit wax within thehydrocarbon production facility. In other embodiments, the pump may beoperated to inhibit asphaltene within the hydrocarbon productionfacility. In other embodiments, the pump may be operated to inhibithydrates within the hydrocarbon production facility. In otherembodiments, the pump may be operated to treat or inhibit scale withinthe hydrocarbon production facility.

In step 112, the pump may be operated to compare the effectiveness of atreatment operation of each of a first chemical and a second chemicalcarried by the skid. Thus, a first chemical form a first chemical tankmay be injected into the hydrocarbon production facility and the effectof the first chemical on the hydrocarbon production facility may beevaluated. Thereafter, a second chemical from a second chemical tank maybe injected into the hydrocarbon production facility and the effect ofthe second chemical on the hydrocarbon production facility may beevaluated, after which, the chemical with the most desirable effects cancontinue to be utilized without the need to retrieve the skid or deployadditional equipment. In this regard, based on the evaluation andeffectiveness of the two chemicals, one chemical may be selected forlong term treatment of the hydrocarbon production facility, whereasanother chemical may be selected for short term treatment of thehydrocarbon production facility, and thus, the pump may be operatedaccordingly first to inject one chemical for a short term treatment andthe other chemical for a long term treatment. As used herein, short termand long term are relative and are simply utilized to distinguish ashorter period of time from a longer period of time. In someembodiments, a third chemical tank having a third chemical is loweredwith the first and second chemical tanks; and the ROV is utilized tooperate the chemical injection skid in order to inject the thirdchemical into the hydrocarbon production facility, after which, similarto above, the effect of the third chemical on the hydrocarbon productionfacility may be evaluated and the most desirable chemical for a desiredeffect may be selected, again, without the need for retrieving the skidor deploying additional equipment, all of which can be costly and timeconsuming. In one or more embodiments, at least one of the chemicals ishighly viscous chemical. In one or more embodiments, at least one of thechemicals is a long chain compound. In embodiments where two or morechemical are evaluated, the two or more chemicals may be the samechemical with different formulations.

In step 114, a chemical preparation mechanism may be lowered with theskid and operated for a particular function. In one or more embodiments,a chemical preparation mechanism carried by the skid may be operated torecirculate chemicals contained within a chemical tank so as reduce thelikelihood of settling of the constituent components of the chemicals.In some embodiments, this recirculation may continue to occur evenduring chemical injection operations, while in other embodiments, itwill be appreciated that the step of recirculating chemicals containedwithin a chemical tank may be carried out before the step of injectingthe chemical into the hydrocarbon production facility. Operating achemical preparation mechanism to mix a first chemical carried in afirst tank on the skid and second chemical carried in a second tank onthe skid together prior to the step of injecting.

In one or more embodiments of step 114, a chemical preparation mechanismcarried by the skid may be operated to mix two or more chemicals priorto injection of the mixture into the hydrocarbon production facility.Thus, a first chemical taken from a first tank on the skid may be mixedwith a second chemical taken from a second tank on the skid.

It will be appreciated that a subsea chemical injection system such asthe embodiments described above can be quickly mobilized, deployed onthe seabed and operated, giving cost effective and timely chemicalinjection for a short to medium term: typically from a few days toseveral months. The system may be a temporary installation atsignificantly less cost than permanent systems. This is particularlyuseful where there is uncertainty on the effectiveness of chemicaltreatment and/or short remaining field life, thus permitting a trialsystem for a short duration with a low investment. The trial allowsfurther allows for an informed decision regarding the most efficientlonger term chemical injection scheme without the foregoing costs.Moreover, because the system is deployed more rapidly than existingsubsea chemical injection systems, it allows for benefits to be morequickly realized. Benefits can include increased production, avoidanceof flow restriction/blockages, reduction in corrosion etc. This can alsogenerate early additional revenue or reduce cost.

Thus, a system for treating subsea hydrocarbon production facilities hasbeen described. The system includes a non-buoyant skid suspended from afirst cable configured to support the weight of the skid, the skidincluding a chemical injection pump and a chemical tank mounted thereon;and a remotely operated vehicle independent of the skid and attached toa second umbilical, wherein the remotely operated vehicle is configuredto couple the pump to the subsea hydrocarbon production facilities.Likewise, in another embodiment, the system includes a skid suspendedfrom a first cable configured to support the weight of the skid, theskid including a chemical injection pump, a first chemical tank and asecond chemical tank, all mounted on the skid; and a remotely operatedvehicle independent of the skid and attached to a second umbilical,wherein the remotely operated vehicle is configured to couple the pumpto the subsea hydrocarbon production facilities. Similarly, a chemicalinjection skid for deployment to a subsea hydrocarbon productionfacility has been described. The skid includes a skid frame; a chemicaltank mounted on the skid frame; and a chemical injection pump mounted onthe skid frame and in fluid communication with the chemical tank,wherein said chemical injection pump is adapted to inject a lower volumeof viscous chemical into a subsea hydrocarbon production facility.

Any one of the foregoing embodiments may include any one or more of thefollowing elements, alone or in combination with other elements:

-   -   At least two chemical tanks mounted on the skid frame.    -   At least two chemical tanks mounted on the skid.    -   The skid frame, chemical tank and chemical injection pump        comprise a non-buoyant structure.    -   The skid is non-buoyant.    -   A first level on which the chemical tank is mounted and a second        level above the chemical tank to which the chemical injection        pump is mounted.    -   The skid comprises a first level on which the chemical tank is        mounted and a second level above the chemical tank to which the        chemical injection pump is mounted.    -   An electric motor carried by the skid frame and disposed to        drive the pump.    -   An electric motor carried by the skid and disposed to drive the        pump.    -   A first cable supporting the skid frame and a second cable        supporting the ROV.    -   A first cable supporting the skid and a second cable supporting        the ROV.    -   The first cable is non-conducting and the second cable is a        tether.    -   The first cable comprises a conducting electrical cable and the        second cable is a tether.    -   A power supply carried by the skid frame and disposed to power        an electric motor carried by the skid.    -   The skid comprises an on-board power supply carried by the skid        and disposed to power an electric motor carried by the skid.    -   The first cable is an electrical umbilical cable.    -   The on-board power supply is a generator.    -   The on-board power supply is a battery.    -   The chemical tank is a bladder tank.    -   A recirculating or mixing system 36 carried by the skid and in        fluid communication with the tank.    -   A recirculating or mixing system mounted on the skid frame,        wherein the recirculating system is in fluid communication with        the tank.    -   A recirculating or mixing system mounted on the skid, wherein        the recirculating system is in fluid communication with the        tank.    -   The recirculating system is in fluid communication with two or        more tanks.    -   The recirculating system comprises an Archimedes screw within a        tube.    -   The skid further comprises a manipulator arm.    -   The chemical injection pump comprises a low volume metering        pump.    -   A mud mat assembly extending from the skid frame.    -   A mud mat assembly extending from the skid.    -   A control panel operable mounted on the skid frame and operable        by an ROV.    -   A control panel operable mounted on the skid and operable by an        ROV.    -   A seawater filtration system mounted on the skid frame.    -   A seawater filtration system mounted on the skid.    -   The mud mat assembly comprises one or more mud mats extending        outward from a lower portion of skid.    -   The mud mats extend around the periphery of the skid.    -   The mud mat assembly comprises one or more mud mats extending        outward from a lower portion of skid frame.    -   The mud mats extend around the periphery of the skid frame.    -   A first power source and a second power source different from        the first power source.

The first power source is selected from the group consisting of anon-board power source carried by the skid, an electrical cable extendingfrom a surface vessel and power supplied by the ROV; and the secondpower source is selected from the group consisting of an on-board powersource carried by the skid, an electrical cable extending from a surfacevessel and power supplied by the ROV.

The chemical injection line is attached by the ROV to a subsea manifoldor pipeline system. Thus, a method for injecting chemicals into a subseahydrocarbon production facility has been described. The method includeslowering a skid carrying a chemical injection pump and chemical tank toa subsea position adjacent a hydrocarbon production facility; utilizingan ROV to attach a chemical injection line in fluid communication withthe chemical injection pump to an injection point of the hydrocarbonproduction facility; once the chemical injection line has been attached,utilizing the ROV to operate the chemical injection skid in order toinject a chemical from the tank into the hydrocarbon productionfacility. In other embodiments, the method includes lowering a skidcarrying a chemical injection pump, a first chemical tank having a firstchemical and a second chemical injection tank having a second chemicaldifferent from the first chemical to a subsea position adjacent ahydrocarbon production facility; utilizing an ROV to attach a chemicalinjection line in fluid communication with the chemical injection pumpto an injection point of the hydrocarbon production facility; once thechemical injection line has been attached, utilizing the ROV to operatethe chemical injection skid in order to inject the first chemical intothe hydrocarbon production facility and thereafter evaluating the effectof the first chemical on the hydrocarbon production facility; andutilizing the ROV to operate the chemical injection skid in order toinject the second chemical into the hydrocarbon production facility andthereafter evaluating the effect of the second chemical on thehydrocarbon production facility.

Any one of the foregoing embodiments may include any one or more of thefollowing, alone or in combination with other limitations:

-   -   A third chemical tank having a third chemical is lowered with        the first and second chemical tanks; and utilizing the ROV to        operate the chemical injection skid in order to inject the third        chemical into the hydrocarbon production facility and thereafter        valuating the effect of the third chemical on the hydrocarbon        production facility.    -   The skid is lowered on a first cable and the ROV is tethered to        a separate cable.    -   At least two chemical tanks are lowered by the skid, with a        different chemical disposed in each tank.    -   The chemical injection line is attached by the ROV to a        manifold.    -   The chemical injection line is attached by the ROV to a        wellhead.    -   Operating the chemical injection pump to inject the chemical        from the chemical tank into a manifold.    -   Operating the chemical injection pump to inject the chemical        from the chemical tank into a wellhead.    -   Operating the chemical injection pump to inject the chemical        from the chemical tank into a wellbore.    -   Operating the chemical injection pump to treat production        equipment within a wellbore.    -   Operating the chemical injection pump to compare the        effectiveness of each of a first chemical and a second chemical        carried by the skid.    -   Operating the chemical injection pump to improve production        capacity of the hydrocarbon production facility.    -   Operating the chemical injection pump to treat or inhibit        corrosion in the hydrocarbon production facility.    -   Operating the chemical injection pump to inject the chemical        from the chemical tank into a subsea manifold or pipeline        system.    -   Operating the chemical injection pump to treat or inhibit wax        within the hydrocarbon production facility.    -   Operating the chemical injection pump to inhibit asphaltene        within the hydrocarbon production facility.    -   Operating the chemical injection pump to inhibit hydrates within        the hydrocarbon production facility.    -   Operating the chemical injection pump to treat or inhibit scale        within the hydrocarbon production facility.    -   Utilizing a first power source to initiate start-up of the pump        and a second different power source to continue operation of the        pump during pumping.    -   Evaluating the effect of the first chemical on the hydrocarbon        production facility; and utilizing the ROV to operate the        chemical injection skid in order to inject the second chemical        into the hydrocarbon production facility and thereafter        evaluating the effect of the second chemical on the hydrocarbon        production facility.    -   The first power source is selected from the group consisting of        an on-board power source carried by the skid, an electrical        cable extending from a surface vessel and power supplied by the        ROV; and the second power source is selected from the group        consisting of an on-board power source carried by the skid, an        electrical cable extending from a surface vessel and power        supplied by the ROV.    -   Operating the chemical injection pump to pump a first chemical        carried in a first tank on the skid into the hydrocarbon        production facility and evaluating the effect of the first        chemical on the hydrocarbon production facility and thereafter;        operating the chemical injection pump to pump a second chemical        carried in a second tank on the skid into the hydrocarbon        production facility and evaluating the effect of the second        chemical on the hydrocarbon production facility; and based on        the effectiveness of the two chemicals, selecting one chemical        for long term treatment of the hydrocarbon production facility.    -   Operating a chemical preparation mechanism carried by the skid        to recirculate chemicals contained within the chemical tank.    -   Continuing recirculation during chemical injection operations.    -   Prior to the step of injecting, recirculating chemicals        contained within a chemical tank.    -   Operating a chemical preparation mechanism to mix a first        chemical carried in a first tank on the skid and second chemical        carried in a second tank on the skid together prior to the step        of injecting.    -   The step of injecting comprises injecting a mixture of a first        chemical taken from a first tank on the skid and a second        chemical taken from a second tank on the skid.    -   The chemicals are highly viscous chemicals.    -   The chemicals are long chain compounds.    -   The two chemicals are the same chemical with different        formulations.

While various embodiments have been illustrated in detail, thedisclosure is not limited to the embodiments shown. Modifications andadaptations of the above embodiments may occur to those skilled in theart. Such modifications and adaptations are in the spirit and scope ofthe disclosure.

What is claimed is:
 1. A system for treating subsea hydrocarbonproduction facilities comprising: a non-buoyant skid suspended from afirst cable configured to support the weight of the skid, the skidincluding a chemical injection pump and a chemical tank mounted thereon;and a remotely operated vehicle independent of the skid and attached toan umbilical cable, wherein the remotely operated vehicle is configuredto couple the pump to the subsea hydrocarbon production facilities. 2.The system of claim 1, further comprising at least two chemical tanksmounted on the skid.
 3. The system of claim 1, wherein the skidcomprises an on-board power supply carried by the skid and disposed topower an electric motor carried by the skid.
 4. The system of claim 1,wherein the chemical tank is a bladder tank.
 5. The system of claim 1further comprising a recirculating system mounted on the skid, whereinthe recirculating system is in fluid communication with the chemicaltank.
 6. The system of claim 5, wherein the recirculating system is influid communication with two or more tanks.
 7. The system of claim 5,wherein the recirculating system comprises an Archimedes screw within atube.
 8. The system of claim 1, further comprising a control paneloperable mounted on the skid and operable by an ROV.
 9. The system ofclaim 1, further comprising a seawater filtration system mounted on theskid.
 10. The system of claim 1, further comprising one or more mud matsextending outward from a lower portion of skid.
 11. A chemical injectionskid for deployment to a subsea hydrocarbon production facility, thechemical injection skid comprising: a skid frame: a chemical tankmounted on the skid frame; a chemical injection pump mounted on the skidframe and in fluid communication with the chemical tank, wherein saidchemical injection pump is adapted to inject a lower volume of viscouschemical into a subsea hydrocarbon production facility.
 12. The skid ofclaim 11, further comprising at least two chemical tanks mounted on theskid frame.
 13. The skid of claim 12, further comprising a chemicalmixing system mounted on the skid frame, wherein the chemical mixingsystem is in fluid communication with the chemical tank.
 14. The skid ofclaim 13, further comprising a seawater filtration system mounted on theskid frame.
 15. A method for injecting chemicals into a subseahydrocarbon production facility, the method comprising: lowering a skidcarrying a chemical injection pump and chemical tank to a subseaposition adjacent a hydrocarbon production facility; utilizing an ROV toattach a chemical injection line in fluid communication with thechemical injection pump to an injection point of the hydrocarbonproduction facility; and once the chemical injection line has beenattached, utilizing the ROV to operate the skid in order to inject afirst chemical from the tank into the hydrocarbon production facility.16. The method of claim 15, further comprising evaluating an effect ofthe first chemical on the hydrocarbon production facility; and utilizingthe ROV to operate the chemical injection skid in order to inject asecond chemical into the hydrocarbon production facility and thereafterevaluating an effect of the second chemical on the hydrocarbonproduction facility.
 17. The method of claim 15, further comprisingutilizing a first power source to initiate start-up of the chemicalinjection pump and a second power source, different from the first powersource, to continue operation of the chemical injection pump duringpumping.
 18. The method of claim 17 where the first power source isselected from the group consisting of an on-board power source carriedby the skid, an electrical cable extending from a surface vessel andpower supplied by the ROV; and the second power source is selected fromthe group consisting of an on-board power source carried by the skid, anelectrical cable extending from a surface vessel, power supplied by theROV, power supplied by a subsea production system.
 19. The method ofclaim 15, further comprising operating the chemical injection pump topump a first chemical carried in a first tank on the skid into thehydrocarbon production facility and evaluating the effect of the firstchemical on the hydrocarbon production facility and thereafter;operating the chemical injection pump to pump a second chemical carriedin a second tank on the skid into the hydrocarbon production facilityand evaluating the effect of the second chemical on the hydrocarbonproduction facility; and based on the evaluated effect of the first andsecond chemicals on the hydrocarbon production facility, selecting oneof the first and second chemicals for long term treatment of thehydrocarbon production facility.
 20. The method of claim 15, furthercomprising operating a chemical preparation mechanism carried by theskid to recirculate chemicals contained within the chemical tank inorder to maintain the chemicals in a well-mixed, cohesive state andreduce separation of components due to differing specific gravities.